1. Field of the Invention
The invention relates to a device for cold treating a tissue. The invention also relates to an assembly of such a device and a container comprising a cryogenic liquid, such as a spray can. The invention further relates to a method for cold treating a tissue.
2. Background of the Invention
There are different forms of cold treating a tissue. Some of them are aimed at cooling the tissue to a temperature that is above 0 degrees Centigrade. In that case, no damage is caused to the tissue. Other forms are aimed at freezing the tissue, such that under the tissue a blister forms which ensures that the tissue disappears in time. Because this involves purposive damaging of tissue, care is to be devoted to the safety of the treatment.
Freezing of tissue, especially warts, is usually realized by the use of an applicator, which applicator can take up cryogenic liquid and deliver the cryogenic liquid, or the cold generated by evaporation of the cryogenic liquid, to the tissue to be cooled. British patent publication GB2244922 describes an applicator of stainless steel with a hollow space, which can be dipped in liquid nitrogen so that the tip is cooled. The cold applicator tip is thereupon brought into contact with the tissue to be cooled. Another known form of such an applicator is a cotton bud. It absorbs the liquid nitrogen and is then held against the tissue to be cooled. Here, the liquid nitrogen comes into direct contact with the tissue and consequently the procedure should only be performed by an expert. In newer forms that are commercially available and can be performed by anyone, the applicator comprises foam plastic material which can take up cryogenic liquid from a spray can and deliver the cold released upon evaporation of this cryogenic liquid to the tissue to be cooled. Such porous applicators are known for instance from US200510043723 and WO2006/004407. The cryogenic liquid is then chiefly used for cooling the applicator, which applicator thereupon cools the tissue to be cooled. In this way, the cryogenic liquid is not utilized optimally. Moreover, the cold from the applicator in most cases does not come into contact with the entire tissue to be cooled. If the tissue is for instance a wart and the wart forms a protrusion on the skin, then, with this applicator, in practice only the upper side of the tissue is frozen. As a consequence, a frequently occurring problem in treating warts with such an applicator is that only the upper side of the wart disappears and the wart grows again later. A preformed applicator would be too specific for a single shape of a wart and cannot ensure direct contact with a capriciously or aberrantly shaped wart. With a better deformable applicator a part of the tissue surrounding the tissue to be cooled may be wrongly damaged. Yet another disadvantage is that the applicator, with the cryogenic liquid included in it, is not screened from the environment during use, that is, upon movement of the applicator from the container with cryogenic liquid to the tissue to be cooled, so that by accident another part of the skin may be touched, resulting in unwanted damage. In addition, the applicator needs to be saturated with cryogenic liquid for an optimum result, which entails the possibility of drops of cryogenic liquid falling off. A still further disadvantage is that the cold treatment with an applicator is less well reproducible. The force with which the applicator can be pressed against the tissue and the time between the taking up of the cryogenic liquid by the applicator and the application of the applicator to the tissue to be cooled are variable. The foam plastic applicator is marketed together with a spray can to provide the applicator with cryogenic liquid. This spray can comprises a valve which is not dosable. Such a valve, however, entails a considerable chance of hazardous situations because the valve, when improperly used, may be kept depressed continuously, allowing cryogenic liquid thereby released to damage other tissue. Since the valve does not allow of dosing, the amount of cryogenic liquid released is highly variable, which renders the use less reproducible. Typically, to ensure saturation, too much cryogenic liquid will be used.
Freezing a tissue can also be realized by spraying the cryogenic liquid directly onto the tissue to be cooled. This is known, for instance, from WO2005/011560 and EP1586277. In that case, to prevent unwanted damage, the other ambient tissue may be covered or a collar is placed around the tissue to be cooled. The device of WO2005/011560, for instance, can be provided with an end-piece to maintain a minimum distance between spray opening and tissue to be treated. Even so, the risk of improper use and of undesirable damage is so high that this method is therefore to be performed only by an expert. Another important disadvantage of the methods whereby the cryogenic liquid is sprayed directly onto the tissue is that although the surface of the tissue to be cooled cools down rapidly, this effect is rapidly gone again because the cryogenic liquid evaporates rapidly. The cold does not get a chance to penetrate deeply into the tissue. This method is moreover poorly reproducible because the distance from the spraying device to the tissue to be cooled is typically variable and also the ambient temperature and air humidity have a strong influence on the cooling action.
Accordingly, there is a need for a device and a method for reproducibly cold treating a tissue, in particular a wart, which is safe in use and by which the tissue to be cooled is cooled down or frozen deeply into the core. There is also a need for a safe assembly for practicing the cold treatment, which assembly preferably comprises a dosing valve. The object of the present invention is to provide such a solution.